The present invention relates to a method of ultrasonically sealing containers with use of an ultrasonic sealing device for sealing a closure, spout plug or other container component to the main body of the container.
Such an ultrasonic sealing method for containers uses an ultrasonic horn having a sealing action face for sealing a container component to the main body of the container. The sealing action face applies pressure to the portions to be sealed of the container component and the container main body as lapped over each other, and ultrasonic reciprocating vibrations in an axial direction parallel to the direction of application of the pressure are caused to act on the sealing action face.
Also known are other sealing methods which use no ultrasonic sealing device, such as high-frequency induction sealing, high-frequency dielectric sealing and heat sealing with use of a heat plate.
The ultrasonic reciprocating vibrations applied to the horn act on the portions of the container to be sealed as if beating, are therefore transmitted to the wall of the container or to a head space inside the container, and vibrate the contents of the container. This entails the likelihood that the contents will be broken, or the contents will be forced out of the container during sealing by being shaken vigorously or becoming vaporized depending on the conditions involved, if the contents are liquid. To preclude these phenomena, the container needs to have an increased head space.
Furthermore, the conditions for producing satisfactory seals are greatly limited; unless the conditions are fulfilled, a thin wall portion of component of the container will be broken, or pinholes are likely to develop in the seal joint.
In the case where axial ultrasonic reciprocating vibrations are caused to act on the sealing action face for sealing, the sealing operation requires a great pressure. The sealing method is therefore unsuited to containers which are low in buckling strength. In addition, the great pressure must to be received in the vicinity of the portions to be sealed. For this reason, there arises a need to provide a pressure receiving flange on an opening-defining edge portion of the container main body, or an attempt is made to cover the edge portion with a skirted caplike closure. However, when the pressure is to be received by the flange, the skirt becomes an obstacle and can not be formed on the cap, hence limitations on the design of the container and the cap.
Since ultrasonic sealing can not be resorted to for sealing containers of small strength or skirted closures, high-frequency induction sealing or high-frequency dielectric sealing is used, whereas the use of high-frequency sealing requires the use of aluminum or like material which induces high-frequency waves for the portions to be sealed, or the high-frequency dielectric sealing necessitates a material amenable to this method of sealing, hence limitations on the materials for the container or closure and problems to be involved in recycling the material.
The heat sealing operation requires time, is inefficient, and is infeasible for containers and closures having a large thickness.
An object of the present invention is to overcome all the above problems and to provide a method of ultrasonically sealing containers which will not adversely affect the contents of the container during sealing and which can be practiced under widely varying conditions with a high efficiency.
In sealing a container component to a container main body using an ultrasonic horn having a sealing action face, the present invention provides an ultrasonic container sealing method comprising applying pressure to portions to be sealed of the container component and the container main body as lapped over each other by the sealing action face and causing ultrasonic rotational vibration in a rotating direction about an axis parallel to the direction of application of the pressure to act on the sealing action face.
With the ultrasonic container sealing method of the invention, the ultrasonic rotational vibration to be caused to act on the sealing action face does not act as if beating the wall of the container but acts in a direction along the container wall. Accordingly, the vibration produces no adverse effect on the contents during sealing. Furthermore, the pressure to be applied can be small. Moreover, advantages are also available such as a reduction in the wall thickness of containers, savings in resources and cost reductions. The materials for the container body and container components are not limited. For this reason, the container main body and closure can be produced from aluminum-free materials, hence ease of recycling.
When ultrasonic vibration other than the ultrasonic rotational vibration is caused to act on the sealing action face in combination with the rotational vibration, an efficient sealing operation can be performed by utilizing the combined vibrations of ultrasonic waves.
If the sealing action face is provided with indentations and projections in advance for improving the sealing conditions, the sealing operation can be conducted under widely varying conditions.
The container main body may be provided around an edge portion thereof defining an opening with a flange forming the portion to be sealed, and the container component may be in the form of a cap to be fitted over the opening-defining edge portion of the container main body and having a skirt at an outer peripheral edge portion providing the portion to be sealed.
When the pressure to be applied by the ultrasonic horn is received by a bottom of the container main body, the container becomes easy to handle for sealing.